I needed a shared volume across multiple EC2 instances in a VPC. My use case is that multiple "ingress" boxes write files to the shared volume, and then a single "worker" box processes those files. This is a somewhat unusual use case in that it means one box is responsible for 99% of IO heavy operations, and the other boxes are responsible only for writing to the volume, with no latency requirements.

My solution was to mount an EBS on the "worker box," along with an NFS server. Each "ingress box" runs an NFS client that connects to the server via its internal VPC IP address, and mounts the NFS volume to a local directory. It works wonderfully. In three months of running this setup, I've had no downtime or issues, not even minor ones. Granted I don't need any kind of extreme I/O performance, so I haven't measured it, but this system took less than an hour to setup and fit my needs perfectly.